1. Field of the Invention
The present invention is directed to combustion of hydrocarbon fuel and in particular to a burner with a recycle gas duct for use in hydrocarbon fuelled combustion reactors.
2. Description of the Related Art
Burners of a combustion reactant are mainly used for firing gas-fuelled industrial furnaces and process heaters, which require a stable flame with high combustion intensities. Conventionally designed burners include a burner tube with a central tube for fuel supply surrounded by an oxidizer supply port. Intensive mixing of fuel and oxidizer in a combustion zone is achieved by passing the oxidizer through a swirler installed at the burner face on the central tube. The stream of oxidizer is, thereby, given a swirling-flow, which provides a high degree of internal and external recirculation of combustion products and a high combustion intensity.
Recycle gas from a Fisher Tropsh synthesis may cause severe metal dusting when mixed with hot feed gas to a syngas preparation unit, for example to the natural gas feed to an autohermal reformer. Therefore known art mixing arrangements are of complicated mechanical design, using expensive non reliable materials and coatings and/or installation of expensive recycle gas conversion reactor systems.
These problems are solved by the present invention which is a burner comprising means to mix a recycle gas just prior to and in the combustion zone of a catalytic reactor according to the claims, thus avoiding all metal dusting issues related to the above described mixing problems.
US Patent Application Publication No. 2008/0035890 discloses a process to prepare a synthesis gas comprising hydrogen and carbon monoxide comprises performing a partial oxidation on a methane comprising feed using a multi-orifice burner provided with an arrangement of separate passages, wherein the gaseous hydrocarbon having an elevated temperature flows through a passage of the burner, an oxidizer gas flows through a separate passage of the burner and wherein the passage for gaseous hydrocarbon feed and the passage for oxidizer gas are separated by a passage through which a secondary gas flows, wherein the secondary gas comprises hydrogen, carbon monoxide and/or a hydrocarbon.
A swirling burner for use in small and medium scale applications with substantially reduced internal recirculation of combustion products toward the burner face is disclosed in U.S. Pat. No. 5,496,170. The burner design disclosed in this patent results in a stable flame with high combustion intensity and without detrimental internal recirculation of hot combustion products by providing the burner with a swirling-flow of oxidizer having an overall flow direction concentrated along the axis of the combustion zone and at the same time directing the fuel gas flow towards the same axis. The disclosed swirling-flow burner comprises a burner tube and a central oxidizer supply tube concentric with and spaced from the burner tube, thereby defining an annular fuel gas channel between the tubes, the oxidizer supply tube and the fuel gas channel having separate inlet ends and separate outlet ends. U-shaped oxidizer and fuel gas injectors are arranged coaxial at the burner face. The burner is further equipped with a bluff body with static swirler blades extending inside the oxidizer injector. The swirler blades are mounted on the bluff body between their upstream end and their downstream end and extend to the surface of the oxidizer injection chamber.
US Patent Application Publication No. 2002/0086257 describes a swirling-flow burner with a burner tube comprising a central oxidizer supply tube and an outer concentric fuel supply tube, the oxidizer supply tube being provided with a concentric cylindrical guide body having static swirler blades and a central concentric cylindrical bore, the swirler blades extending from outer surface of the guide body to inner surface of oxidizer supply tube being concentrically arranged within space between the guide body and inner wall at lower portion of the oxidizer supply tube.
US Patent Application Publication No. 2007/0010590 describes a process for the production of hydrocarbons including; a) subjecting a mixture of a hydrocarbon feedstock and steam to catalytic steam reforming to form a partially reformed gas, b) subjecting the partially reformed gas to partial combustion with an oxygen-containing gas and bringing the resultant partially combusted gas towards equilibrium over a steam reforming catalyst to form a reformed gas mixture, c) cooling the reformed gas mixture to below the dew point of the steam therein to condense water and separating condensed water to give a de-watered synthesis gas, d) synthesising hydrocarbons from side de-watered synthesis gas by the Fischer-Tropsch reaction and e) separating the hydrocarbons from co-produced water, characterised in that at least part of said co-produced water is fed to a saturator wherein it is contacted with hydrocarbon feedstock to provide at least part of the mixture of hydrocarbon feedstock and steam subjected to steam reforming